Redis : don’t use dbindex if cluster mode

[ldidry]

Hello,

I made a mistake in my configuration and let a dbindex setting for the redis config, but as I am using a Redis cluster, there is no multiple databases so I got this failure:

Failed to setup redis subscription: Redis server refused to switch database- ResponseError
Redis server disconnected, reconnecting in 1s

Nextcloud does not complain as they behave differently between cluster or normal mode (see https://github.com/nextcloud/server/blob/master/lib/private/RedisFactory.php#L79).

I think that notify_push should do the same.

(obviously, I removed the dbindex setting and it works now)